1. Field of the Invention
This invention relates to a novel polyhydroxyalkanoate (hereinafter simply “PHA”), and also relates to a process for producing the PHA, comprising the step of proudcing a PHA by the use of a microorganism having the ability to prdouce the PHA and accumulate it in the bacterial body.
This invention further relates to a charge control agent, a toner binder and a toner for developing electrostatic latent images, used in recording processes which utilize electrophotography, electrostatic recording, magnetic recording or the like, an image-forming method making use of the toner, and an image-forming apparatus therefor. More particularly, it relates to a charge control agent, a toner binder and a toner for developing electrostatic latent images, used in electrophotographic, electrostatic-recording and electrostatic-printing apparatus such as copying machines, printers and facsimile machines, an image-forming method making use of the toner, and an image-forming apparatus therefor. Still more particularly, it relates to a negatively charging charge control agent having higher safety to human bodies and environment, a toner binder and a toner for developing electrostatic latent images, making use of such a charge control agent, an image-forming method making use of the toner, and an image-forming apparatus therefor.
2. Related Background Art
It has hitherto been reported that many microorganisms produce poly-3-hydroxybutyric acid (PHB) or other PHA and accumulate it in the bacterial body (“Handbook of Biodegradable Plastics”, Biodegradable-Plastic Institute, K.K. N•T•S, pp.178-197, 1995). Like conventional plastics, these polyemrs can be utilized for the production of various products by melt processing or the like. Also, since they are biodegradable, they have an advantage of being completely broken down by microorganisms in the natural world, and by no means remain in natural environment to cause pollution as many conventional synthetic polymeric compounds do. They also have superior adaptability to living bodies and are expected to be applicable as medical flexible members.
It is know that such PHAs produced by microorganisms may have various composition and structure depending on the type of microorganisms used for its production, the composition of culture medium, the conditions for culturing and so forth. Researches on how to control such composition and strucutre have hitherto chiefly been made from the viewpoint of the improvement in physical properties of PHAs.
(1) In the first place, as biosyntheses of PHAs by the polymerization of a monomer unit having a relatively simple structure, including: 3-hydroxybutyric acid (hereinafter simply “3HB”), the following cases are available.
(a) Those which contain 3HB and 3-hydroxyvaleric acid (hereinafter “3HV”):
U.S. Pat. Nos. 4,393,167, 4,876,331 and 5,200,332.
(b) those which contain 3HB and 3-hydroxyhexanoic acid (hereinafter “3HHx”);
U.S. Pat. No. 5,292,860 and Japanese Patent Application Laid-Open No. 7-265065.
(c) those which contain 3HB and 4-hydroxybutyric acid (hereinafter “4HB”):
Japanese Patent Application Laid-Open No. 9-191893.
(d) those which contain 3-hydroxyalkanoates having 6 to 12 carbon atoms:
U.S. Pat. No. 5,334,698.
(e) Biosynthesis utilizing a simple fatty acid as a carbon source. Products are substantially the same as those of (d); Appl. Environ. Microbiol., 58(2), 746, 1992.
These are all PHAs each comprised of a monomer unit having an alkyl group in the side chain, i.e., “usual PHA”, all synthesized by β-oxidation of hydrocarbons or synthesis of fatty acids from saccharides by the microorganisms.
(2) When, however, broader application of such PHAs produced by microorganisms, e.g., application as functional polymers is taken into account, a PHA in which a substituent other than the alkyl group has been introduced in the side chain, i.e., “unusual PHA” is expected to very useful. As examples of such a substituent, it may include those containing aromatic rings (such as a phenyl group and a phenoxy group), unsaturted hydrocarbons, an ester group, an ally group, a cyano group, halogenated hydrocarbons and epoxides. Of these, researches are energetically made especially on PHAs having aromatic rings.
(a) Those which contian a phenyl group or a partially substituted phenyl group:
Macromol. Chem. Phys., 191, 1957-1965 (1990) and Macromolecuels, 24, 5256-5260 (1991) report that Pseudomonas oleovorans produces a PHA containing 3-hydroxy-5-phenylvaleric acid as a unit, using 5-phenylvaleric acid as a substrate.
Macromolecules, 29, 1762-1766 (1996) reports that Pseudomonas oleovorans produces a PHA containing 3-hydroxy-5-(4′-tolyl)valeric acid as a unit, using 5-(4′-tolyl)valeric acid as a substrate.
Macromolecules, 32, 2889-2895 (1999) reports that Pseudomonas oleovorans produces a PHA containing 3-hydroxy-5-(2′,4′-dinitrophenyl)valeric acid and 3-hydroxy-5-(4′-nitrophenyl)valeric acid as units, using 5-(2′,4′-dinitrophenyl)valeric acid as a substrate.
(b) Those which contain a phenoxyl group or a partially substituted phenoxyl group:
Macromol. Chem. Phys., 195, 1665-1672 (1994) reports that Pseudomonas oleovorans produces a PHA copolymer of 3-hydroxy-5-phenoxyvaleric acid with 3-hydroxy-9-phenoxynonanoic acid, using 11-phenoxyundecanoic acid as a substrate.
Japanese Patent No. 2,989,175 discloses invention which is concerned with a homopolymer comprised of a 3-hydroxy-5-(monofluorophenoxy)pentanoate (3H5(MFP)P) unit or a 3-hydroxy-5-(difluorophenoxy)pentanoate (3H5(DFP)P) unit, and a copolymer containing at least the (3H5(MFP)P) unit or the (3H5(DFP)P) unit; Pseudomonas putida capable of synthesizing such a polymer; and a process of producing the above polymer by the use of the genus Pseudomonas. It is reported that as its effect a polymer the side-chain terminal of which has a phenoxyl group substituted with 1 or 2 fluorine atom(s) can be synthesized by utilizing a long-chain fatty acid having a substituent and that stereo-regularity (syndiotacticity) and water repellency can be imparted having a high melting point and retaining good processability.
In addition to such fluorine-group-substituted products, cyano-group- or nitro-group-substituted products are also on researches.
Can. J. Microbiol., 41, 32-43 (1995) and Polymer International, 39, 205-213 (1996) report that a PHA containing 3-hydroxy-p-cyanophenoxyhexanoic acid or 3-hydroxy-p-nitrophenoxyhexanoic acid as a monomer unit is produced using octanoic acid and p-cyanophenoxyhexanoic acid or p-nitrophenoxyhexanoic acid as a substrate by the use of Pseudomonas oleovorans strain ATCC 29347 and Pseudomonas putida strain KT 2442.
These reports are useful in order to obtain polymers which all have an aromatic ring in the side chain of PHA, different from the commonly available PHAs having an alkyl gorup in the side chain, and have physical properties arising therefrom.
(3) As a new category, without limitation merely to changes in physical properties, researches are also made intending to produce a PHA having a suitable functional group in the side chain.
For example, Macromolecules, 31, 1480-1486 (1996) and Journal of Polymer Science: Part A: Polymer Chemistry, 36, 2381-2387 (1998) report that a PHA contianing at the side-chain terminal a unit having a vinyl group is synthesized and thereafter the product synthesized is epoxidized with an oxidizing agent and this has enabled synthesis of a PHA containing a highly reactive epoxy group at the side-chain terminal.
Besides the vinyl group, as an example of synthesizing a PHA containing a unit having a thioether (—S—; a sulfanyl linkage), expected to provide a high reactivity, Macromolecules, 32, 8315-8318 (1999) reports that Pseudomonas putida strain 27N01 produces a RNA copolymer of 3-hydroxy-5-thiphenoxyvaleric acid (3-hydroxy-5-(phenylsulfanyl)valeric acid) with 3-hydroxy-7-thiophenoxyheptanoic acid (3-hydroxy-7-(phenylsulfanyl)heptanoic acid), using 11-thiophenoxyundecanoic acid (11-(phenylsulfanyl)undecanoic acid) as a substrate.
A number of methods are also conventionally known as methods for electrophotography. In general, copied images are obtained by forming an electrostatic latent image on an image-bearing member (photosensitive member) by utilizing a photoconductive material and by various means, subsequently developing the latent image by the use of a toner to form a visible image (toner image), transferring the toner image to a transfer medium as occasion cells, and then fixing the toner image to the transfer medium by heating and/or pressing. As methods by which the electrostatic latent image is formed into a visible image, cascade development, magnetic bruch development, pressure development and so foruth are known in the art. Another method is also known in which, using a magnetic toner and a rotary developing sleeve provided with magnetic poles at the core, the magnetic toner is caused to fly from the developing sleeve to the photosensitive member by the an electric field.
As development methods used when electrostatic latent images are developed, available are a two-component development method making use of a two-component type developer comprised of a toner and a carrier and a one-component development method making use of no carrier and comprised only of a toner.
Here, fine colored particles commonly called a toner are constituted of a binder resin and a colorant as essential components and besides optionally a magnetic material and so forth. As methods for imparting electric charges to the toner, the charging properties of the binder resin itself may be utilized without use of any charge control agent. If that is the case, however, the binder resin has poor charging stability with time and poor moisture resistance. Accordingly, a charge control agent is usually added for the purpose of charge retention and charge control of the toner.
Conventional charge control agents nowadays known in the present technical field include, e.g., as negative charge cotnrol agents, are dye metal complexes, metal complexes of aromatic dicarboxylic acids and metal complexes of salicylic acid derivatives. Also, known as positive charge control agents are Nigrosine dyes, triphenylmethane dyes, organotin compounds such as quaternary ammonium salt dibutylin oxides of various types, and so forth. toners containing any of these as charge control agents, however, do not necessarily well satisfy quality characteristics such as charging performance and stability with time in some cases, depending on their composition; the characteristics being required in toners.
For example, toners containing the azo dye metla complexes known as negative charge control agents are on a reasonable level in respect of the highness of charge quantity. However, since the azo dye metal complexes are crystal compounds with a low molecular weight, they may have a poor dispersibility depending on the type of binder resins in which they ar eto be incorproated. In such a case, the negative charge contorl agents are not uniformly distributed in the binder resins, and the resultant toners also have a charge quantity distribution lacking in sharpness greatly, so that the images to be obtained may have a low gradation, showing a poor image formation performance. Moreover, the azo dye metal complexes have color tone specific thereto, and hence, under the existing conditions, they are used only in toners with hues limited mainly to black. When such toners are used as color toners, what is of a great problem is that they have not any sharpness of coloring agents which is required in order to obtain images having a high requirement for color tone.
As an example of nearly colorless negative charge control agents, the metal complexes of aromatic dicarboxylic acids are available, which, however, may have a problem of low dispersibility becuase of the fact that they are not perfectly colorless and that they are crystal compounds with a low molecular weight.
As for the Nigrosine dyes and the triphenylmethane dyes, known as positive charge control agents, they stand colored in themselves, and hence, under the existing conditions, they are also used only in toners with hues limited mainly to black, and also may have no good stability with time when such toners are used in continuous copying. Conventional quaternary ammonium salts may also have an insufficient moisture resistance when incorporated in toners. In such a case, such toners may have so poor a stability with time as not to afford any good images in their repeated use.
In recent years, from the viewpoint of environmental conservation, too, what has become a worldwide subject of discussion is how waste be curtailed and how the safety of waste be improved. Such a subject is likewise discussed also in the field of electrophotography. More specifically, with wide spread of image-forming apparatus, the disposal of printed paper, waste toner after use and copying paper is increasing year by year, and the safety of such waste is also an important subject from the standpoint of the conservation of global environment.
Taking account of such a point, studies are being made on polymer type charge control agents. They include compounds disclosed in, e.g., U.S. Pat. Nos. 4,480,021, 4,442,189 and 4,925,765 and Japanese Patent Application Laid-Open Nos. 60-108861, 61-3149, 63-38958 and 63-88564. Also, in general, as polymer type charge control agents used when toners are made to exhibit negative chargeability, there are many examples in which copolymers of styrene and/or α-methylstyrene with alkyl acrylates or methacrylates or alkyl acrylate or methacrylate amides having sulfonic acid groups are used (Japanese Patent Application Laid-Open Nos. 7-72658 and 8-17964 and Japanese Patent Nos. 2,114,410, 2,623,684 and 2,807,795). Such materials are advantageous in that they are colorless, but must be added in a large quantity in order to ensure charge quantity.
Thus, these compounds do not have any sufficient performance as charge control agents, and have problems on charge quantity, charging-rise performance, stability with time, environmental stability and so forth. Also, considering not only the aspect of function but also any influence on human bodies and enviroment, it is strongly sought in respect of compounds and organic solvents used in synthesis, too, to provide a safer compound, a safer and milder syntehsis process, and a charge control agent hwihc can achieve use of organic solvents in a smaller quantity.
From the viewpoint of environmental conservation, development is being made on resins degradable with time by the action of microorganisms, i.e., biodegradable resins. For example, as stated previously, it has been reported that many microorganisms are capable of producing the biodegradable resin PHA and accumulating it in the bacterial body. It is known that such PHA can have various composition and structure depending on the type of microorganisms used for its production, the composition of culture medium, the conditions for culturing and so forth. Researches on how to control such composition and structure have hitherto chiefly been made from the viewpoint of the improvement in physical properties of PHA. With regard to its application, too, they have already given reasonable actual results especially in the field of materials for medical use. In the field of agriculture, too, the biodegradable resins are used in multifiles, gardening material and so forth, and also in sustained-release agricultural chemicals, fertilizers and so forth. In the field of leisure industry, too, the biodegradable resins are used in fishing lines, fishing articles, golf goods adn so forth.
However, considering their wide application as plastics, under the existing conditions they can not still be said to be satisfactory in respect of physical properties. In order to make the PHA utilizable in much wider ranges, it is important to study the improvement of physical properties more widely. For that end, it is essential to make development and research on PHAs containing monomer units of various structures. Meanwhile, the PHA of the type a substituent has been introduced in the side chain can be expected to be expanded as a “functional polymer” having very useful functions and properites attributable to the properties of the substituent introduced, by selecting according to the desired properties and so forth the substituent to be introduced. Namely, it is also an important subject to make development and research on such a superior PHA that can achieve both such functional factors and the biodegradability.
In the field of electrophotography, too, the applciation of biodegradable resins to binder resins is proposed especially in the production of toners. For example, U.S. Pat. No. 5,004,664 discloses a toner having as its composition a biodegradable resin, in particular, polyhydroxybutyric acid, polyhydroxyvaleric acid, or a copolymer or blend of these. Japense Patent Application Laid-Open No. 6-289644 also disclose an electrophotographic toner particularly used for heat-roll fixing, which is characterized in that at least a binder resin contains a vegetable wax and a biodegradable resin (as exemplified by polyesters produced by microorganisms and natural polymeric materials derived from vegetables or animals), and the vegetable wax is added to the binder resin in an amount of from 5 to 50% by weight.
U.S. Pat. No. 5,667,927 also discloses an electrophotographic toner characterized by containing a lactic-acid resin as a binder resin. Japanese Patent Application Laid-Open No. 9-274335 still also discloses a toner for developing electrostatic latent images which is characterised by containing a polyester resin and a colorant; the former being obtained by dehydration polycondensation of a composition containing lactic acid and a tri- or more functional oxycarboxylic acid.
Japanese Patent Application Laid-Open No. 8-262796 also discloses an electrophotographic toner containing a binder resin and a colorant, and is characterized in that the binder resin comprises a biodegradable resin (as exemplified by aliphatic polyester resins) and the colorant comprises a water-insoluble coloring matter. Japanese Patent Application Laid-Open No. 9-281746 still also discloses a toner for developing electrostatic latent images which is characterized by containing a urethanated polyester resin and a colorant; the former being obtained by cross-linking polylactic acid with a tri- or more functional polybasic isocyanate.
In all the electrophotographic toners stated above, biodegradable resins are used as their binder resins, and they are understood to have the effect of contributing to the environmental safeguard and so forth.
However, any report on an example in which biodegradable resins are used in charge control agents is still unknown. Thus, there is room for further progress in respect of the contribution to te environmental safeguard and so forth.
As stated previously, in the PHAs produced by microorganisms, those having various composition and strucutre are obtained by changing the type of microorganisms used for its production, the composition of culture medium, the conditions for culturing and so forth. However, considering their wide application as plastics, they can not still be said to be satisfactory in respect of physical properties. In order to make the PHA utilizable in much wider ranges, it is important to study the improvement of physical properties more widely. For that end, it is essential to make development and research on PHAs containing monomer units of various structures, on their production processes and on microorganisms capable of producing the desired PHAs efficiently.
Meanwhile, as also stated previously, the PHA of the type a substituent has been introduced in the side chain (the unusual PHA) can be expected to be expanded as a “functional polymer” having very useful functions and properties attributable to the properties of the substituent introduced, by selecting according to the desired properties and so forth the substituent to be introduced. Thus, it is also an important subject to make development and research on such a superior PHA that can achieve both the functional factors and the biodegradability, on its production process and on microorganisms capable of producing the desired PHA efficiently.
More specifically, where PHAs in the side chains of which various substituents have been itnroduced are produced by microorganisms, a method is used in which, as is seen in the reports given previously on Pseudomona soleovorans, an alkanoate having a substituent intended to be introduced is utilized also as a carbon source for proliferation in additoin to its utilization as a raw material for polymers.
However, in the method in which an alkanoate having a substituent intended to be introduced is utilized also as a carbon source for proliferation in additoin to its utilization as a raw material for polymers, it is expected that an energy source on the basis of the formation of acetyl-CoA by β-oxidation is supplied from the alkanoate. In such a method, the acetyl-CoA can not be formed by β-oxidation unless the substrate has a chain length which is large to a certain extent. Hence, it is of a great problem that the alkanoate usable as the substrate of PHA is necessarily limited. Also, commonly, substrates whose chain length has come short for two methylene chains each as a result of β-oxidation are newly formed, and these are incorporated as monomer units of the PHA. Hence, the PHA synthesized may often be a copolymer comprised of monomer units whose chain length differs for two methylene chains each. In the resports given previously, produced is a copolymer comprised of three monomer units, 3-hydroxy-8-phenoxyoctanoic acid derived from 8-phenoxyoctanoic acid which is a substrate, 3-hydroxy-6-phenoxyhexanoic acid which is a by-product derived from a metabolic intermediate and 3-hydroxy-4-phenoxybutyric acid. In this regard, it is very difficult to use this method when it is intended to obtain a PHA comprised of single monomer units. Moreover, in the method which conditions that an energy source on the basis of the formation of acetyl-CoA by β-oxidation is supplied, microorganisms may proliferate so slowly that it takes a time to synthesize the PHA and that the PHA synthesized tends to be in a low yield. These are also of great problems. Accordingly, it is considered effective to use a method in which microorganisms are cultured in a culture medium where, in place of the alkanoate having a substituent to be introduced, a medium-chain fattya cid or the like such as octanoic acid or nonanic acid is made present together (coexistent) as a carton source for proliferation, and thereafter the PHA is extracted. Such a method is commonly used.
However, according to studies made by the present invention, the PHA synthesized through β-oxidation, using the medium-chain fatty acid or the like such as octanoic acid or nonanoic acid as the carbon source for proliferation as in the above may be obtained in a low purity, and 50% or more of the polymer obtained is held by 3-hydroxyalkanoic acid monomer units of mcl (hereinafter often simply “mcl-3HA”), i.e., the units of “usual PHA”, which are monomer units derived from the carbon source for proliferation (e.g., 3-hydroxyoctanoic acid and 3-hydroxynonanoic acid). These mcl-3HA monomer units are polymers which are tacky at normal temperature when composed alone, and may make polymers have a greatly low glass trnasition temperature (Tg) when mixedly present in a large quantity in the PHA intended in the present invention. Hence, where physical properties of polymers which are hard at normal temperatureare to be attained, it is not prefrable that the mcl-3HA monomer units are mixedly present.
It is also known that such heterogeneous side-chain strucutre may obstruct the intramolecular or intermolecular mutual action attributable to the side-cahin structure to greatly affect crystallizability or orientationality. For the achievement of improvement in physical properties of polymers and impartment of functional performance thereto, it is of a great problem that such mcl-3HA monomer units are mixedly present. As a means for solving this problem, a purification step for separating and removing any “unintended” monomer units such as the mcl-3HA monomer units derived from the carbon source for proliferation may be provided in order to botain a PHA constituted of only monomer units having specific substituents. This, however, brings about problems that its operation is complicated and also a greatly low yeild may inevitably result. A greater problem is that, where the intended monomer units an the unintended monomer units have formed a polymer, it is very difficult to remove only the unintended monomer units. Especially where it is intended to synthesize a PHA containing such monomer units that have as side-chain sturcture a group obtained from an unsaturated hydrocarbon, an ester group, an allyl gorup, a cyano group, a nitro group, a group obtained from a halogenated hydrocarbon or a group into which an epoxide has been introduced, the mcl-3HA monomer units often form a copolymer together with the intended monomer units. Thus, it is very difficult to rmeove the mcl-3HA monomer units after the synthesis of PHA.
Accordingly, the present inventors have come acknowledged that, when the application to functional polymers is taken into account, it is by all means necessary to make development of a biosynthetic process by which the “unusual PHA” can be obtained in a high purity. Thus, it has been considered very useful and important to make development of i) a superior polymer having both the functional performance and the biodegradability as stated above, ii) microorganisms capable of producting such a polymer and accumulating it in the bacterial body, and iii) a process for bio-synthesizing the PHA in a high purity and efficiently.